US3091151A - Electromechanical oscillators - Google Patents

Description

May 1963 J. A. CUNNlNGHAM 3,091,151

ELECTROMECHANICAL OSCILLATORS Filed Nov. 18. 1960 W9 7 5 I 25 fa INVENTOR.

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" atenr 3,091,151 Patented May 28, 1963 iiice 3,091,151 ELECTROMEC-HANICAL OSQILLATORS John A. Cunningham, Batavia Township, Kane County, Ill. (Rte. 1, Box 7, Batavia, Ill.) Filed Nov. 18, 1960, Ser. No. 70,190 2 Claims. (Cl. 84-457) This invention relates to improvements in electromechanical oscillators and more particularly to the novel construction and assembly of :a unit wherein the vibrating element will oscillate at a constant frequency irrespective of temperature variations.

In many applications, mechanical oscillators, such as tuning forks, are employed to generate an alternating current of substantially constant frequency and usually are driven by electro-magnetic means. The vibrating frequency of tuning forks changes with variations in the temperature of the tuning fork and its associated magnets. The main causes for such variations are the changes that occur in the dimensions and elasticity of the tines of the fork and changes in the strength of the magnetic fields of the magnets. An increase in length, a decrease in elasticity or a decrease in the strength of the magnetic field will result in a lowering of the pitch or vibration frequency of the tuning fork tines; whereas a decrease in its length, increase in its elasticity or an increase in the strength of the magnetic field will raise the pitch or vibration frequency.

Any increase or decrease in temperature is directly related to the magnetic influence from the electro-magnets with which the times are associated. When the air gap between the pole pieces of the electromagnetic driving means and the free end of the tuning fork tines is adjusted to a certain critical distance, a constant vibration frequency irrespective of temperature is obtained. Thus, if the air gap between the electro-magnet and tuning fork tine is greater than the critical distance, an increase in temperature will result in an increase in the frequency (a positive temperature vs. frequency coefficient). However, if the air gap is less than the critical distance, an increase in temperature will result in a decrease in frequency (a negative temperature vs. frequency coefiicient). Once the critical air gap is determined and the adjustment locked in place, changes in temperature no longer result in changes in frequency, and a zero temperature vs. frequency coeflicient is obtained.

The representative oscillator herein disclosed is characterized by the inclusion of a resonator in any accep table form, such as a tuning fork, disposed in association with electro-magn'et driving and pick-up means, which means are adjustable, or at least the magnetic cores of which are adjustable, relative to the tines, so as to vary the air gap between the tines and cores to thereby control the induced eddy currents by a change of the magnetic influence of the electromagnetic means and alter the temperature vs. frequency coeflicient.

Fine tuning or minute influencing of the temperature coefficient is accomplished herein by the novel construction of the electromagnetic driving and pickup means, or the cores thereof, which are independently or jointly adjustable to vary the air gaps between the driven and pick-up faces of the tines and the influencing magnetic cores. More specifically, if a tuning fork answers a prescribed temperature coefiicient versus frequency test and measurements of a specific value, this value can be changed by use of the herein disclosed structure in either a positive or a negative direction from zero.

When the air gap is greater than the critical gap, a reduction in the air gap between the tines and the electromagnetic means will increase the eddy currents and influence the temperature coeiiicient value in a positive direction causing the temperature coefiicient versus frequency curve to either come closer to zero from a negative area or to go further from zero in a positive direction to a more positive area. A positive coeflicient of fre: quency versus temperature will cause the tines to change frequency by an increase of frequency with an increase of temperature.

When the air gap is less than the critical gap, an increase in the air gap and the resulting decrease of the eddy currents will change the temperature coefficient value in a negative direction causing the temperature coefficient versus frequency curve to either move from the zero area to a more negative area or to approach more closely the zero area from a positive area and become less positive. A negative coefficient of frequency versus temperature will cause the tines to change frequency by a reduction or lowering of frequency with an increased temperature.

The herein disclosed resonator is structurally designed to assist in producing an effective zero coefficient of frequency versus temperature for the resonator and it is one of the objects of the invention to provide such a device.

Another object is to provide an electromechanical oscillator wherein micrometric adjustment may be made in the gap between the electro magnet core and the tines of the resonator.

With the foregoing and such other objects and advantages in view, which will appear as the description proceeds, the invention consists of certain novel features of construction, arrangement and combination of parts hereinafter fully described, illustrated in the accompanying drawings, and particularly pointed out in the appended claims, it being understood that various changes in form, proportion, size and minor details may be made without illustrating the principles of the invention.

Referring to the drawings in which the same characters of reference are employed to identify corresponding parts:

FIG. 1 is a plan view of a representative oscillator illustrating the principals of the invention.

FIG. 2 is an enlarged transverse sectional view taken on line 22 of FIG. 1.

FIG. 3 is a graphic representation of a curve showing a negative coefficient of temperature versus frequency.

FIG. 4 is a graphic representation of a curve showing a positive coefficient of temperature versus frequency.

FIG. 5 is a graphic representation of a constant frequency.

Referring to the exemplary embodiment of the invention disclosed in the accompanying drawings, the electromechanical oscillator shown in FIG. 1 comprises a base or mounting block 11 longitudinally slotted inwardly from one end, as at 12, and recessed on its top face at the unslotted end to receive a resonator or temperature compensated tuning fork 13, the tines 14 of which extend into slot 12. Screws or rivets 15 secure the base end of the tuning fork in the recess.

A pair of upstanding bosses 16 are located laterally one on each side of slot 12. Each of these bosses mounts an electro-magnet assembly, generally indicated at 17, so arranged that the core 18 of each has one of its ends of poles spaced closely to the respective driven and pick up faces of tines 14 of the tuning fork.

As is well understood in this art, an increase in the gap between the cores 18 and the tines 14 will increase the frequency of the tuning fork oscillations, whereas a de crease in the gap will reduce the frequency of the tuning fork oscillations. Consequently, each electro magnet is mounted in the boss for adjustment toward and away from the tuning fork so as to adapt the assembly for adjustment to alter the size of the gaps between their cores and the respective tines in order to arrive at the critical air gap adjustment for a zero temperature frequency coefficient.

Referring now particularly to FIG. 2, each magnetic core 18 preferably has its mounted end screw threaded, as at 21, for threading it through its mounting boss so as to be adjusted axially upon being rotated in either direction. Preferably, the threads are generated with precision so that micrometric adjustment can be attained and determined by rotating the cores a predetermined amount. For example, by providing forty (40) threads per inch, there will be a change of .025 inch in the position of the core for each rotation. Obviously, the electromagnetic coils 22 may be mounted upon the magnetic cores in any conventional manner. The axial adjustment once determined is fixed by set screws 26 in the top of the bosses 16.

As previously discussed, if the oscillating frequency of the tuning is lowered by an increase in its temperature it is said to have a negative coefficient of temperature versus frequency. Also, if this same increase of temperature causes the frequency of the tuning fork to rise, the fork is said to have a positive coefficient of temperature versus frequency.

Either effect causes a change in the rate of oscillating frequency, a condition that is obviated by the present arrangement which allows the gap between the electro magnet cores and the opposed surfaces of the tuning fork tines to be adjusted to the critical air gap. This can perhaps be best illustrated by the following test results.

A mechanical oscillator was caused to operate at a given temperature and the oscillating frequency of the tines was recorded as was also the gap between the tines and the cores. With these conditions remaining constant, the rate of frequency change resulting from heating of the tuning fork was recorded in either a positive or a negative direction. In the instant test, the tuning fork was determined to have a negative coeflicient of 100 parts per million over a temperature range of C. to plus 100 C. This is a frequency change of .001 cycle per second per degree centigrade. In FIG. 3, the line 23 is representative of this condition.

The gaps between the tines and the cores were decreased by .001 of an inch and the test repeated. This produced a positive coefiicient of temperature versus frequency of the same rate as was present in the negative 4 direction, but in the positive direction. This is illustrated by line 24 in FIG. 4.

Readjustment of the gaps was continued until the critical gaps were established that produced a zero coefficient of temperature versus frequency, although the temperature of the tuning fork ranged from 0 C. to plus C. With these temperature variations, the oscillating frequency remained constant, as illustrated by line 25 in FIG. 5, within the limits of employed audible frequency determinating equipment and temperature measuring equipment.

As many possible embodiments may be made in the invention, and as many changes might be made in the embodiment selected forillustration, it is to be understood that all matters hereinbefore set forth and shown are to be interpreted as illustrative and not in a limiting sense.

What I claim and desire to secure by Letters Patent of the United States is:

-1. In combination with a tuning fork, single pole electromagnet controlling the vibration of said fork, the pole faces of said electromagnets being located near the free ends of the tines of said tuning fork, and means to adjust the pole faces of the electromagnets toward and away from the tines to obtain the critical air gap to maintain an effective zero coefficiency of frequency versus temperature for the tuning fork.

2. In combination with a tuning fork having a given coefiicient of elasticity, an electromagnet controlling the vibrations of said tuning fork, said electro magnet comprising a single core having an electric coil therearound, the core of said electrom-agnet having its magnetic pole spaced from one of the tines of said fork, a mounting for said electro magnet including a boss, and said core being threaded into said boss so as to be adjustable toward and away from the tines to decrease or increase the gap between its pole and the time and control the eddy current loss for influencing the temperature coefficient.

References Cited in the file of this patent UNITED STATES PATENTS 1,637,442 Dorsey Aug. 2, 1927 2,384,823 Eisenhour Sept. 18, 1945 2,928,308 Godbey Mar. 15, 1960 FOREIGN PATENTS 636,563 Great Britain May 3, 1950

Claims (1)

1. IN COMBINATION WITH A TUNING FORK, SINGLE POLE ELECTROMAGNET CONTROLLING THE VIBRATION OF SAID FORK, THE POLE FACES OF SAID ELECTROMAGNETS BEING LOCATED NEAR THE FREE ENDS OF THE TIMES OF SAID TUNING FORK, AND MEANS TO ADJUST THE POLE FACES OF THE ELECTROMAGNETS TOWARD AND AWAY FROM THE TIMES TO OBTAIN THE CRITICAL AIR GAP TO MAINTAIN AN EFFECTIVE ZERO COEFFICIENCY OF FREQUENCY VERSUS TEMPERATURE FOR THE TUNING FORK.

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